An electric drive can serve as the only drive for the motor vehicle or it can be provided in addition to an internal combustion engine. In such a case, the electric drive and the internal combustion engine can each drive the motor vehicle on its own or, superimposed on one another, they can drive the motor vehicle jointly. Such drive concepts are referred to as hybrid drives.
Normally, an electric drive comprises an electric motor and, downstream thereto, a reduction gear unit which translates a rotational movement from a fast speed to a slow speed. From the reduction gear unit, the torque is transmitted to the driveline of the motor vehicle. For this, a differential drive arranged in the torque flow downstream the reduction gear unit divides the introduced torque to two output shafts for driving the motor vehicle wheels. The two output shafts of the differential drive have a differential effect relative to each other, i.e. if one of the two output shafts rotates more quickly, the other output shaft rotates correspondingly more slowly, and vice versa.
From FR 2 946 292 A3 a driving unit is known with two electric motors, two primary driveshafts, two intermediate shafts, two reduction gear units, and one differential drive. Each of the two reduction gear units is drivingly connected to differential drive, so that both reduction gear units are able to transmit torque to the differential drive. Between each driveshaft and the associated intermediate shaft there are provided two switchable sets of gears with different reduction ratios. A synchronising device is provided between the gear sets.
DE 10 2012 204 717 A1 proposes an drive assembly with an electric motor for a motor vehicle with a first electric machine and a first driveshaft, a second electric machine with a second driveshaft and a transmission with a planetary gear set, a spur gear unit and an output. The spur gear unit comprises a first set of gear with a first transmission ratio, a second set of gears with a second transmission ratio, and a shift unit. The shift unit can be switched into a first position in which the first gear of the first set of gears is connected to the first driveshaft and into a second position in which the first gear of the second set of gears is connected to the first driveshaft.
From FR 2 946 292 A3 a drive assembly is known with an electric motor, a reduction gear unit with two parallel shafts and a differential drive. The reduction gear unit comprises two set of gears for transmitting torque between the two parallel shafts. There is provided a double clutch which is able to transmit a torque introduced by the electric motor optionally to the respective drive gear of one of the two sets of gears.
WO 2012/087700 A1 proposes an electric drive module with an electric motor, a planetary drive, a synchronising unit, a reduction gear unit and a differential assembly. The sun gear of the planetary drive and the drive gear of the synchronising unit are connected to one another via a hollow shaft. The hollow shaft comprises radial bores.
Electric drives of the mentioned type with multi-step transmissions with clutch shift unit require a major constructional effort for the clutches and actuators. A multi-step transmission with a synchronising unit requires high switching forces, thus involving high demands to be met by the actuator.